In communication fields, RF frequencies are often used as carriers for signal receiving and transmission. Using current techniques in the receiver, modulated RF frequency signals are received and filtered to attenuate interference, especially image signals, before being down converted to intermediate frequency (IF) frequencies. In the transmitter, filtering is also needed before the signals are transmitted, in order to reduce their interferences to communication channels and the receiving side of the circuits. In either of the receiving and transmitting processes, due to the strict signal filtering requirements, filtering components, such as filters and duplexers, usually cannot be made using normal inductors and capacitors, especially those which can be integrated into semiconductor ICs. Instead, components using, for example, dielectric resonators, surface acoustic wave elements and the like are needed. While these components works well, they are bulky in size, expensive, sensitive to manufacturing and assembly tolerances and are difficult to integrate into ICs. This is one of the major obstacles to integrate a circuit system into a single chip. Zero IF techniques used in receivers solved effectively the image interference problem. However, its application has been limited to certain types of systems, due to issues such as DC offset, sensitivities, and the like, which lower the performance of the receivers and require demanding compensation and processes.
It is an object of this invention to provide a methodology for RF frequency signal processing for receiving and transmission that solve the above problems associated with the current techniques.